A wide variety of LED drivers or regulators are known for use in providing flash lighting for cameras. For example, Semtech (SC4501 data sheet) provides current control, but requires external loop compensation and restricts the dynamics of the converter. Such a current regulator is also analog, not digital, and requires many components which compromise the efficiency of the regulator. Such decreased efficiency requires excessive power consumption which is highly detrimental for portable, battery-operated applications, such as for use in cameras and mobile telephones.
Prior art LED drivers generally have very low efficiency, making them highly unsuitable for applications in portable devices such as cameras and mobile telephones. For example, in U.S. Pat. No. 6,317,566, an electronic flash device uses current supplied from a battery through a current-limiting resistor, increasing power dissipation and rendering the device very inefficient. It is also a complex device, using many components, including using a three-winding transformer for functional needs when isolation is not achieved.
Similarly, in U.S. Patent Publication No. 2005/0265709, current is also supplied through a resistor to the LEDs of a camera flash, in either a continuous low current mode or a temporary high current mode, also thereby increasing power dissipation and making this device quite inefficient.
Lastly, in U.S. Pat. No. 7,136,672, current is also supplied through selectable resistors to the LEDs of a camera flash, used with a camera of a mobile telephone. The LEDs utilized emit red, green, and blue (RGB) light, and are connected to ground via a switch and a resistor, with different resistor values utilized to adjust current levels through the LEDs. Again, such use of current-limiting resistors serves to increase power dissipation and render the resulting device considerably less power efficient.
Accordingly, a need remains for a driver circuit or current regulator for solid state lighting which can provide multiple modes of operation, such as for supplying power to light-emitting diodes utilized for flash or background lighting in cameras and other portable devices. Such a current regulator should provide digital control, without requiring external compensation. Lastly, such a current regulator should utilize comparatively fewer components, providing reduced cost and size, while simultaneously increasing its efficiency and enabling longer battery life when used in portable devices.